Cancer sufferers are suing the NHS after they were forced to buy their own life-prolonging drugs, it emerged today.

Hundreds of patients have forked out thousands of pounds for drugs after NHS bosses ruled they were not 'cost effective' - even though they can extend a dying person's life or help ease suffering in their final days.

Now one patient has been reimbursed after a decision not to fund treatment was overturned at appeal - and dozens of others are threatening to sue.

Health Secretary Alan Johnson is awaiting the results of a review into restrictions on NHS patients topping up their treatments with private drugs

Current rules mean patients cannot top up NHS treatment with expensive private drugs, if they are not available on the Health Service. If they do so, they have to pay for the cost of the rest of their NHS treatment.

The furore over the banning of so-called 'top up' payments forced health secretary Alan Johnson to commission a review by cancer czar Mike Richards, which is due to report next week.

The review is expected to back top ups in limited circumstances - and will be used by those who have already paid for treatment to support their cases in court.

And last week the Daily Mail revealed that the National Institute for health and Clinical Excellence, the drug rationing watchdog, was changing its rules which could mean more life-prolonging drugs are deemed cost effective.

Now an investigation in London found that at least three of the city's 31 primary care trusts were facing claims from patients for money back.

The Patients Association said these claims were likely to be the 'tip of the iceberg'.

Spokeswoman Katherine Murphy said: 'The numbers will be far higher once this is more of an open issue and once people know about it.

'People have gone to great lengths, sometimes having to sell their homes to pay for treatments which have been denied to them.

'These are people who are very ill and they are having to pay twice - they've already paid for the NHS through taxes and now they are having to pay again because it is not there for them when they need it. It's unforgivable.'

Bromley PCT, in south east London, said it had already compensated one patient for drugs which it initially refused to fund - although it is not known which type of drug.

A kidney cancer patient has demanded a refund from Hillingdon PCT after he paid for the life-extending drug Sorafenib. The trust us facing a number of further inquiries about refunds.

Wandsworth PCT has also received a written request for a refund - and its chairman Ian Reynolds believes that court action was inevitable from patients who have had drugs turned down.

He said: 'We're being sent bills by people turned down by exceptional treatment panels and who have then gone private. We're not liable to pay but the reality is that these claims will now end up in court.'

A spokesman for the Department of Health said: 'We know there is variation in how individual trusts are applying the current guidance, and that is why the Secretary of State asked Professor Mike Richards, national clinical director for cancer, to lead a review into this difficult issue.

'Professor Richards is looking at how a consistent approach across the country might be best achieved.'